Power take-off transmissions are used on, among other things, agricultural vehicles such as haulers or tractors, but also on construction machinery and commercial vehicles, in order to provide the drive of a power take-off driven by the engine propelling the corresponding vehicle. Mechanisms which are attached to or trailed from the corresponding vehicle can be mechanically driven by means of the power take-off. Power take-off transmissions usually have a hydraulically operable clutch, via which the power take-off shaft can be brought into driving connection with the drive shaft of the power take-off transmission. The drive shaft is usually connected to the engine propelling the vehicle or to a drive train connected the propelling engine. The hydraulic coupling of the power take-off transmission usually has a clutch plate set, which is brought into frictional connection through the application of pressure to a hydraulically operable annular piston and can thereby be activated or closed, so that a drive moment supplied by the drive shaft is transferred to the power take-off shaft. When operating the power take-off transmission, particularly when operating the clutch, in other words, during the application of pressure to the annular piston and the creation of frictional connections in the clutch plate set resulting from this, the clutch and other transmission components warm up. Heat is thereby generated, which must be removed via the hydraulic fluid used both to operate the clutch and also to lubricate the transmission components. A power take-off transmission of this kind usually has a corresponding hydraulic supply or hydraulic assembly for this purpose, which comprises a hydraulic cooler, wherein the hydraulic liquid circulates continuously and is pumped out of a hydraulic reservoir or out of a transmission sump through the hydraulic cooler.
It is known that a hydraulic supply of this kind can be designed such that a first hydraulic line connects the hydraulic pump to the piston and a second hydraulic line branching off from the first hydraulic line connects the hydraulic pump to the hydraulic cooler, wherein a hydraulic supply to the annular piston is controlled via a proportional valve and parallel thereto a continuous circulation of hydraulic fluid through the hydraulic cooler is achieved by a pressure control valve disposed in the second hydraulic line. The clutch plate set is cooled by lubrication with the cooled hydraulic fluid and by the clutch plate set being connected to the transmission sump. However, cooling of this kind exhibits a relatively low cooling capacity and can only guarantee heat dissipation to some extent. Particularly where higher-powered transmissions are concerned, larger clutches or clutch plate sets have to be used, in order to guarantee the required heat dissipation. This is at variance with efforts currently being made to achieve a small overall size with greater power.
In order to improve the cooling capacity, it has been suggested that additional cooling circuits should be created, which enable the transmission and clutch to be cooled by separate channels in the corresponding components and using a hydraulic circuit separate from the hydraulic supply for the piston for activating the clutch. This is in turn complicated in terms of design, requires a large number of parts and is cost-intensive.
Thus the problem addressed by the disclosure is seen as being that of specifying a power take-off transmission of the kind mentioned above, by means of which the aforementioned problems can be overcome. In particular, the cooling capacity is to be improved without significantly increasing the structural complexity.